Today single device can run multiple applications and give multiple services such as email, web, video, audio and instant messaging. Data from each of these applications has packaged, transported and delivered to the right application on the destination device. The transport Layer (Layer 4) of the OSI model also accepts data from the application Layer and prepare it for addressing at-the network layer. A sending device communicates with a receiving device to make a decision how to split data into segments, how to make possible data sending without losing any Segment, how to confirm all the segments arrived at receiving the device.

The transport Layer is responsible for end-to-end communication over a network. It also provides logical communication between application processes running on different hosts within a layered architecture of protocols and other network components.

Functions of the Transport Layer

Following are the functions of the transport layers.

Connection management

Segmentation

Reliable and unreliable data delivery

Flow control as well as connection multiplexing

It also makes possible to allow multiple applications to work at-the same time to send and receive data.

Data transmission method can be connection-oriented or connectionless according to need. Connectionless uses UDP and connection-oriented uses TCP.

The sequence numbers and acknowledgments (ACKs) used for reliability.

Reliable connection Controls flow through the uses of windowing or acknowledgments.